Wireless communication device and method for controlling transmission power

ABSTRACT

Disclosed is a wireless communication device that can suppress an increase in power consumption of a terminal while preventing the degradation of SINR measurement precision resulting from TPC errors in a base station. A terminal ( 100 ) controls the transmission power of a second signal by adding an offset to the transmission power of a first signal; an offset-setting unit ( 106 ) sets an offset correction value in response to a transmission time gap between a third signal transmitted the previous time and the second signal transmitted this time; and a transmission power control unit ( 111 ) controls the transmission power of the second signal using the correction value.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus and amethod of controlling transmission power.

BACKGROUND ART

In an uplink for 3GPP LTE (3rd Generation Partnership Project Long TermEvolution, hereinafter referred to as LTE), estimation of the channelquality between a terminal (user equipment, UE) and a base station (BSor eNB) using a sounding reference signal (SRS) is supported. The SRS isused mainly for scheduling of an uplink data channel (physical uplinkshared channel, PUSCH) (e.g. frequency resource assignment and selectionof a modulation and coding scheme (MCS)). “Sounding” refers toestimation of the channel quality between a terminal and a base station.

In LTE, similar transmission power control (TPC) is performed for aPUSCH and an SRS. Specifically, transmission power of SRS(SRStransmission power) is determined by adding an offset to transmissionpower of a PUSCH (PUSCH transmission power). For example, in LTE, SRStransmission power P_(SRS)(i) in subframe #i is determined by thefollowing Equation 1.P _(SRS)(i)=min{P _(CMAX) ,P _(SRS) _(—) _(OFFSET)+10 log₁₀(M _(SRS))+P_(O) _(—) _(PUSCH)+α·PL+f(i)}  (Equation 1)

In Equation 1, P_(CMAX) [dBm] denotes maximum transmission power of anSRS that can be transmitted from a terminal; P_(SRS) _(—) _(OFFSET)[dBm] denotes an offset value for transmission power of a PUSCH to betransmitted from the terminal (parameter set by a base station); M_(SRS)denotes the number of frequency resource blocks to be assigned to theSRS; P_(O) _(—) _(PUSCH) [dBm] denotes the initial value of the PUSCHtransmission power (parameter set by the base station); PL denotes apath loss level [dB] measured by the terminal; a denotes a weightcoefficient indicating the compensation ratio of the path loss (PL)(parameter set by the base station); and f(i) denotes an accumulatedvalue in subframe #i containing past TPC command (control values such as+3 dB, +1 dB, 0 dB, and −1 dB) in closed loop control.

Meanwhile, standardization of LTE-Advanced, which is a developed versionof LTE, is started. In LTE-Advanced, support for uplink transmission inwhich a terminal uses a plurality of antennas (single user-multipleinput multiple output, SU-MIMO) is being studied. The SU-MIMO is atechnique in which a single terminal transmits data signals in a certainfrequency at a certain time from a plurality of antennas tospatial-multiplex the data signals through a virtual communication path(stream) in a space.

In order to perform communication by SU-MIMO in LTE-Advanced, a basestation must know the status of a propagation path between each antennaof a terminal and each antenna of the base station. Hence, the terminalmust transmit an SRS to the base station from each antenna.

Regarding the uplink for LTE-Advanced, a technique is being studied inwhich common transmission power control is employed among a plurality ofantennas of a terminal in order to control transmission power of a PUSCHand an SRS (for example, see NPL 1). Specifically, at the terminal, asingle value is used as each parameter in the equation for determiningSRS transmission power, which is shown as Equation 1, uniformly for allantennas. This can prevent an increase in signaling load required fortransmission power control at a terminal having a plurality of antennas.

CITATION LIST Non-Patent Literature

NPL 1

-   R1-101949, Huawei, “Uplink Multi-Antenna Power Control”

SUMMARY OF INVENTION Technical Problem

Meanwhile, when the reception SINR (signal to interference and noiseratio) of an SRS transmitted from a terminal to a base station(reception level of SRS at a base station) decreases to a certain level,the measurement accuracy of the channel quality (e.g. SINR measurementvalue) using SRSs between the base station and the terminal (SINRmeasurement accuracy) is significantly deteriorated due to an influenceof interference and noise.

For example, FIG. 1 shows a simulation result indicating characteristicsof the SINR measurement value of SRS (vertical axis) at a base stationin relation to the reception. SINR of SRS at the base station (inputSINR [dB], horizontal axis). As shown in FIG. 1, when the input SINR ofSRS is greater than 0 dB, the input SINR and the SINR measurement valueare substantially the same values (indicated by the dashed line in FIG.1), showing good SINR measurement accuracy at the base station. Bycontrast, as shown in FIG. 1, when the input SINR of SRS is 0 dB orless, an error (or variance) between the input SINR and the SINRmeasurement value is large, showing bad SINR measurement accuracy.

If the SINR measurement accuracy of SRS is deteriorated, the basestation cannot perform precise scheduling of a PUSCH (such as frequencyresource assignment and MCS selection), impairing the systemperformance.

Furthermore, when transmission power is controlled at a terminal, theSRS transmission power actually transmitted by the terminal may deviatefrom the target SRS transmission power set to the terminal. That is, atthe terminal, an error occurs between the target SRS transmission powerset to the terminal and the SRS transmission power actually transmittedby the terminal (hereinafter referred to as “TPC error”). Hence, if theSRS transmission power actually transmitted by the terminal is smallerthan the target transmission power due to the TPC error, the receptionSINR of SRS at the base station may decrease to a certain level (0 dB orless in FIG. 1), impairing the SINR measurement accuracy, as describedabove.

To prevent deterioration of the SINR measurement accuracy of SRS causedby the TPC error, a method may be employed in which the SRS transmissionpower is controlled by taking into consideration the variation of theTPC error. That is, the terminal sets the SRS transmission power suchthat the SRS transmission power is greater than the target transmissionpower by an assumed maximum TPC error. For example, the terminalincreases offset value P_(SRS) _(—) _(OFFSET) for PUSCH transmissionpower shown in Equation 1 by adding the assumed maximum TPC error to theoffset value. This prevents the reception SINR of SRS at the basestation from decreasing to a certain level (not 0 dB or less in FIG. 1)even when the terminal receives the influence of the TPC error incontrolling the SRS transmission power. Thus, deterioration of the SINRmeasurement accuracy can be prevented.

In this method of controlling SRS transmission power, however, greaterSRS transmission power must be assigned to the terminal as the assumedmaximum TPC error is greater, regardless of the actual TPC error. Thisincreases power consumption of the terminal. In addition, anotherproblem will arise in which an increase in SRS transmission power leadsto an increase in inter-cell interference. Furthermore, if the commontransmission power control is performed for a plurality of antennas whenthe terminal has the plurality of antennas as described above, SRStransmission power transmitted from all antennas increases as theassumed maximum TPC error increases. Thus, a problem of increased SRStransmission power and increased inter-cell interference becomes morenoticeable.

It is an object of the present invention to provide a radiocommunication apparatus and a method of controlling transmission powerthat can reduce an increase in power consumption of a terminal whilepreventing deterioration of the SINR measurement accuracy caused by theTPC error at a base station.

Solution to Problem

A radio communication apparatus according to a first aspect of thepresent invention adds an offset value to transmission power of a firstsignal to control transmission power of a second signal, the radiocommunication apparatus including: a setting section that determines acorrection value for the offset value according to the transmissionperiod or the difference of transmission power between a third signaltransmitted and the succeeding second signal to be transmitted; and acontrol section that uses the correction value to control thetransmission power of the second signal.

A method of controlling transmission power in a radio communicationapparatus that adds an offset value to transmission power of a firstsignal to control transmission power of a second signal according to asecond aspect of the present invention, the method including:determining a correction value for the offset value according to thetransmission period or the difference of transmission power between athird signal transmitted and the succeeding second signal to betransmitted; and using the correction value to control the transmissionpower of the second signal.

Advantageous Effects of Invention

According to the present invention, an increase in power consumption ofa terminal can be reduced while deterioration of the SINR measurementaccuracy caused by the TPC error is prevented at a base station.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing characteristics of a SINR measurement value ofSRS in relation to input SINR of SRS at a base station;

FIG. 2 is a block diagram of a configuration of a terminal according toEmbodiment 1 of the present invention;

FIG. 3 is a block diagram of a configuration of a base station accordingto Embodiment 1 of the present invention;

FIG. 4 shows a correspondence between elapsed time T and a correctionvalue for an offset value according to Embodiment 1 of the presentinvention;

FIG. 5 shows a correspondence between an SRS transmission period and acorrection value for an offset value according to Embodiment 1 of thepresent invention;

FIG. 6 is a block diagram of a configuration of a terminal according toEmbodiment 2 of the present invention;

FIG. 7 shows a correspondence between power difference ΔP and acorrection value for an offset value according to Embodiment 2 of thepresent invention;

FIG. 8 is a block diagram of a configuration of a terminal according toEmbodiment 3 of the present invention;

FIG. 9 shows a correspondence between the type of SRS and an offsetvalue according to Embodiment 3 of the present invention;

FIG. 10 shows a correspondence between the type of SRS and an offsetvalue according to Embodiment 3 of the present invention;

FIG. 11 shows a correspondence between the type of SRS and an offsetvalue according to Embodiment 3 of the present invention;

FIG. 12 is a block diagram of another internal configuration of anoffset setting section according to the present invention;

FIG. 13 shows another correspondence among elapsed time T, powerdifference ΔP, and a correction value for an offset value according tothe present invention;

FIG. 14A shows the allowable range of the TPC error in LTE (in the caseof T>20 ms);

FIG. 14B shows the allowable range of the TPC error in LTE (in the caseof T≦20 ms);

FIG. 15 shows another correspondence among elapsed time T, powerdifference ΔP, and a correction value for an offset value according tothe present invention;

FIG. 16 is a block diagram of another configuration of a terminalaccording to the present invention (in the case where the terminal has aplurality of antennas);

FIG. 17 shows another correspondence between elapsed time T and acorrection value for an offset value according to the present invention;and

FIG. 18 shows another correspondence between power difference ΔP and acorrection value for an offset value according to the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. A terminal (radiocommunication apparatus) according to the embodiments of the presentinvention controls SRS transmission power by adding an offset value toPUSCH transmission power as shown in Equation 1.

Embodiment 1

FIG. 2 shows a configuration of terminal 100 according to the presentembodiment. At terminal 100 in FIG. 2, RS generation section 101generates an RS sequence (SRS. For example, Zadoff-Chu (ZC) sequence)and outputs the generated RS sequence to phase rotation section 102.

Phase rotation section 102 performs phase rotation on the RS sequencereceived from RS generation section 101 and outputs the RS sequenceafter the phase rotation to mapping section 103, the phase rotationcorresponding to a time domain cyclic shift amount (amount of cyclicshift (CS), not shown) instructed from the base station. Because samplesof the RS sequence are assigned to subcarriers, the RS sequence is afrequency domain signal. Hence, the phase rotation process in thefrequency domain in phase rotation section 102 is equivalent to a cyclicshift process in the time domain.

Mapping section 103 maps the RS sequence after the phase rotationreceived from phase rotation section 102 on a plurality of subcarriers,which are frequency resources, based on frequency resource assignmentinformation (not shown) instructed from the base station, and outputsthe mapped RS sequence to inverse fast Fourier transform (IFFT) section104.

IFFT section 104 performs an IFFT process on the plurality ofsubcarriers in which the RS sequence is mapped and outputs the signalafter the IFFT process to cyclic prefix (CP) addition section 105.

CP addition section 105 adds a signal identical to the tail of thesignal after the IFFT process from IFFT section 104 to the head of thesignal as a CP and outputs the resulting signal with the CP (SRS) totransmission section 109 (D/A section 110).

Offset setting section 106 includes elapsed-time calculation section 107and offset value determination section 108. Offset setting section 106determines an offset value for the PUSCH transmission power (hereinafterreferred to as “transmission power offset value,” i.e. a valuecorresponding to P_(SRS) _(—) _(OFFSET) shown in Equation 1). The offsetvalue is used to determine transmission power of the RS sequence (SRS).

Specifically, elapsed-time calculation section 107 calculates an elapsedtime between the transmission time of the uplink channel (e.g. uplinksignal such as a PUSCH, a PUCCH and an SRS) transmitted from terminal100 and the transmission time of the succeeding SRS to be transmittedfrom the terminal. Then, elapsed-time calculation section 107 outputsthe calculated elapsed time to offset value determination section 108.

Offset value determination section 108 first determines an correctionvalue for the offset value (i.e. P_(SRS) _(—) _(OFFSET) in Equation 1)according to the elapsed time received from elapsed-time calculationsection 107, the offset value being instructed from the base station.Then, offset value determination section 108 corrects the offset valueinstructed from the base station using the determined correction value,thereby determining the transmission power offset value. Then, offsetvalue determination section 108 outputs the transmission power offsetvalue to transmission section 109 (transmission power control section111). The process of setting the transmission power offset value inoffset setting section 106 will be explained in detail later.

Transmission section 109 includes D/A section 110, transmission powercontrol section 111, and up-conversion section 112. Transmission section109 performs a transmission process such as D/A conversion,amplification, and up-conversion on the signal (SRS) from CP additionsection 105.

Specifically, D/A section 110 of transmission section 109 performs D/Aconversion on the signal (SRS) from CP addition section 105 and outputsthe signal (SRS) after D/A conversion to transmission power controlsection 111.

Transmission power control section 111 uses the transmission poweroffset value from offset value determination section 108 to controltransmission power of the signal with CP from D/A section 110, andoutputs the signal (SRS) after the transmission power control toup-conversion section 112. That is, transmission power control section111 uses the correction value for the offset value determined in offsetvalue determination section 108 to control the SRS transmission power.

Up-conversion section 112 frequency-converts the signal after thetransmission power control from transmission power control section 111into the carrier wave frequency. Then, up-conversion section 112transmits the frequency-converted signal after the transmission processfrom antenna 113. Through this process, the SRS is transmitted with thetransmission power controlled in transmission power control section 111.

For example, according to the present embodiment, SRS transmission powerP_(SRS)(i) in subframe #i is determined by the following Equation 2.P _(SRS)(i)=min{P _(CMAX),(P _(SRS) _(—) _(OFFSET)+Δ_(offset))+10log₁₀(M _(SRS))+P _(O) _(—) _(PUSCH)(j)+α(j)·PL+f(i)}  (Equation 2)

In Equation 2, P_(CMAX) [dBm] denotes maximum transmission power of anSRS that can be transmitted from terminal 100; P_(SRS) _(—) _(OFFSET)[dBm] denotes the offset value for transmission power of a PUSCH to betransmitted from terminal 100 (parameter set by a base station); M_(SRS)denotes the number of frequency resource blocks to be assigned to theSRS; P_(O) _(—) _(PUSCH) [dBm] denotes the initial value of the PUSCHtransmission power (parameter set by the base station); PL denotes apath loss level [dB] measured by terminal 100; α denotes a weightcoefficient indicating the compensation ratio of path loss (PL)(parameter set by the base station); f(i) denotes an accumulated valuein subframe #i containing past TPC command (control values such as +3dB, +1 dB, 0 dB, and −1 dB) in closed loop control. Furthermore, inEquation 2, Δ_(offset) denotes a correction value for offset valueP_(SRS) _(—) _(OFFSET) that is associated with the elapsed timecalculated in elapsed-time calculation section 107.

That is, offset value determination section 108 determines correctionvalue Δ_(offset) for correcting offset value P_(SRS) _(—) _(OFFSET)instructed from the base station based on the elapsed time calculated inelapsed-time calculation section 107, as shown in Equation 2. Then,offset value determination section 108 adds correction value Δ_(offset)to offset value P_(SRS) _(—) _(OFFSET) to determine transmission poweroffset value (P_(SRS) _(—) _(OFFSET)+Δ_(offset)), as shown in Equation2. Transmission power control section 111 controls SRS transmissionpower P_(SRS)(i) in accordance with Equation 2, using transmission poweroffset value (P_(SRS) _(—) _(OFFSET)+Δ_(offset)) received from offsetvalue determination section 108.

FIG. 3 shows a configuration of base station 200 according to thepresent embodiment. In base station 200 in FIG. 3, reception section 202receives a signal transmitted from terminal 100 (FIG. 2) via antenna 201and performs a reception process such as down-conversion and A/Dconversion on the received signal. The signal transmitted from terminal100 contains an SRS. Then, reception section 202 outputs the signalafter the reception process to CP removal section 203.

CP removal section 203 removes the CP added to the head of the signalafter the reception process from reception section 202 and outputs thesignal without CP to fast Fourier transform (FFT) section 204.

FFT section 204 performs an FFT process on the signal without CP from CPremoval section 203 to convert the signal into the frequency domainsignal and outputs the frequency domain signal to demapping section 205.

Demapping section 205 extracts a signal (i.e. SRS) corresponding to thetransmission band (frequency resources) of a desired terminal (desiredterminal subject to communication) from the frequency domain signalreceived from FFT section 204, based on the frequency resourceassignment information for the desired terminal instructed from basestation 200 to terminal 100. Then, demapping section 205 outputs theextracted signal (SRS) to section 207 for measuring SINR for SRS(SRSSINR measurement section 207).

Cyclic shift amount setting section 206 outputs a cyclic shift amount ofterminal 100 (desired terminal), which is instructed from base station200 to terminal 100, to SRS SINR measurement section 207.

SRS SINR measurement section 207 performs complex division on the SRSfrom demapping section 205 and the RS sequence known by the transmittingand receiving sides to determine a correlation signal in the frequencydomain. Then, SRS SINR measurement section 207 performs the inversediscrete Fourier transform (IDFT) process on the correlation signal inthe frequency domain to calculate the correlation signal in the timedomain (i.e. delay profile). This delay profile contains SRSs of aplurality of terminals. Thus, SRS SINR measurement section 207 uses theamount of cyclic shift of the desired terminal received from cyclicshift amount setting section 206 to mask part of the delay profile otherthan the part corresponding to the amount of cyclic shift of the desiredterminal, thereby calculating the SINR measurement value of the SRS(SINR measurement value for SRS) of the desired terminal. Then, SRS SINRmeasurement section 207 outputs the calculated SINR measurement valuefor SRS to section 209 for deriving SINR for data (data SINR derivingsection 209).

Offset setting section 208 performs the same process as offset settingsection 106 of terminal 100. That is, offset setting section 208determines an offset value of transmission power for PUSCH (transmissionpower offset value, i.e. (P_(SRS) _(—) _(OFFSET)+Δ_(offset)) shown inEquation 2). The offset is used to determine the transmission power ofSRS to be transmitted from terminal 100 (desired terminal). That is,offset setting section 208 determines correction value Δ_(offset) foroffset value P_(SRS) _(—) _(OFFSET) according to the elapsed timebetween the transmission time of the uplink channel transmitted from thedesired terminal and the transmission time of the succeeding SRS to betransmitted from the terminal, and determines transmission power offsetvalue (P_(SRS) _(—) _(OFFSET)+Δ_(offset)). Then, offset setting section208 outputs the determined transmission power offset value (P_(SRS) _(—)_(OFFSET)+Δ_(offset)) to data SINR deriving section 209.

Data SINR deriving section 209 uses the SINR measurement value for SRSfrom SRS SINR measurement section 207 and the transmission power offsetvalue from offset setting section 208 to derive SINR of uplink data(i.e. PUSCH) (SINR measurement value for data). Specifically, data SINRderiving section 209 uses transmission power offset value (P_(SRS) _(—)_(OFFSET)+Δ_(offset)) to derive the SINR measurement value for data inaccordance with the following equation 3.SINR measurement value for data SINR measurement value for SRS−(P _(SRS)_(—) _(OFFSET)+Δ_(offset))  (Equation 3)

Then, base station 200 performs scheduling of terminal 100 (e.g.frequency resource assignment and MCS selection) using, for example, theSINR measurement value for data derived in data SINR deriving section209.

In base station 200, channel quality deriving section 210 includingcyclic shift amount setting section 206, SRS SINR measurement section207, offset setting section 208, and data SINR deriving section 209 maybe configured.

Next, the process of setting the transmission power offset value inoffset setting section 106 of terminal 100 (FIG. 2) will now beexplained in detail.

The temperature of a power amplifier (PA) of terminal 100 varies as timeelapses. Thus, the amplification characteristics of the PA varies astime elapses. For this reason, the longer a transmission time intervalbetween uplink channels (uplink signal including a PUSCH, a PUCCH, andan SRS) is, the more significantly the amplification characteristics ofthe PA of terminal 100 varies. That is, it is assumed that an increaseof the transmission time interval between uplink channels leads to anincrease in the TPC error.

That is, in terminal 100, the TPC error varies depending on the elapsedtime (transmission time interval) between the transmission time of theuplink channel and the transmission time of the succeeding uplinkchannel. Specifically, the TPC error decreases as the elapsed timebetween the transmission time of the uplink channel and the transmissiontime of the succeeding uplink channel (transmission time interval)decreases.

Hence, offset setting section 106 determines an transmission poweroffset value ((P_(SRS) _(—) _(OFFSET)+Δ_(offset)) shown in Equation 2),which is used to determine the SRS transmission power, according to theelapsed time (transmission time interval) between the transmission timeof the uplink channel and the transmission time of the succeeding SRS.

In the following explanation, terminal 100 uses the equation oftransmission power shown in Equation 2 to calculate SRS transmissionpower P_(SRS)(i). P_(SRS) _(—) _(OFFSET) shown in Equation 2 isdetermined with reference to an assumed maximum TPC error. That is,P_(SRS) _(—) _(OFFSET) shown in Equation 2 is a parameter determined toreduce or prevent the deterioration of the SINR measurement accuracy ofSRS at base station 200 even when the assumed maximum TPC error occurs.Furthermore, P_(SRS) _(—) _(OFFSET) shown in Equation 2 is reported(instructed) from base station 200 to terminal 100. In the followingexplanation, the TPC error is defined as “small” if elapsed time(transmission time interval) T between the transmission time of theuplink channel and the transmission time of the succeeding SRS is 20 msor less, and the TPC error is defined as “large” if elapsed time T islonger than 20 ms.

Elapsed-time calculation section 107 calculates elapsed time T betweenthe transmission time of the uplink channel and the transmission time ofthe succeeding SRS.

Next, offset value determination section 108 determines correction valueΔ_(offset) for offset value P_(SRS) _(—) _(OFFSET) instructed from basestation 200 according to elapsed time T calculated in elapsed-timecalculation section 107.

For example, as shown in FIG. 4, offset value determination section 108sets correction value Δ_(offset) to −6 dB in the case of elapsed time Tof 20 msec or less (the TPC error is small), and sets correction valueΔ_(offset) to 0 dB in the case of elapsed time T longer than 20 msec(the TPC error is large). Then, offset value determination section 108adds correction value Δ_(offset) to offset value P_(SRS) _(—) _(OFFSET)instructed from base station 200 to determine transmission power offsetvalue (P_(SRS) _(—) _(OFFSET)+Δ_(offset)).

That is, in the case where offset value P_(SRS) _(—) _(OFFSET)instructed from base station 200 is determined with reference to anassumed maximum TPC error, offset value determination section 108 setscorrection value Δ_(offset) to 0 dB in the case of longer elapsed time T(T>20 ms in FIG. 4) and uses offset value P_(SRS) _(—) _(OFFSET)instructed from base station 200 as the transmission power offset valuewithout change. On the other hand, offset value determination section108 determines correction value Δ_(offset) to −6 dB in the case ofshorter elapsed time T (T≦20 ms in FIG. 4) and corrects offset valueP_(SRS) _(—) _(OFFSET) instructed from base station 200 into a smallervalue, and thus sets the smaller value than offset value P_(SRS) _(—)_(OFFSET) as the transmission power offset value.

As described above, terminal 100 sets a different correction value forthe offset value instructed from base station 200 according to thetransmission time interval (elapsed time T) between the uplink channeltransmitted and the succeeding SRS to be transmitted. Specifically,terminal 100 determines correction value Δ_(offset) such that SRStransmission power P_(SRS)(i) in the case of shorter elapsed time T(T≦20 ms in FIG. 4, i.e. the TPC error is small) is smaller than SRStransmission power P_(SRS)(i) in the case of longer elapsed time T (T>20ms in FIG. 4, i.e. the TPC error is large). That is, terminal 100 setssmaller SRS transmission power P_(SRS)(i) for shorter elapsed time T.

As described above, the TPC error decreases as elapsed time T decreases.For this reason, when terminal 100 sets smaller SRS transmission powerfor shorter elapsed time T (T≦20 ms in FIG. 4), there is a lowprobability that the reception SINR decreases to a certain level (0 dBor less in FIG. 1) due to the influence of the TPC error. Thus, the SINRmeasurement accuracy at base station 200 is less likely to bedeteriorated.

That is, terminal 100 can set the SRS transmission power down to anecessary minimum value with which a desired reception SINR can beacquired at base station 200 by correcting the offset value instructedfrom base station 200 according to elapsed time T. Here, the desiredreception SINR refers to reception SINR with which the SINR measurementaccuracy is not deteriorated. With this configuration, the SINRmeasurement accuracy of SRS (measurement accuracy of channel quality) atbase station 200 can be ensured while power consumption at terminal 100is reduced to a necessary minimum. In other words, determination ofappropriate SRS transmission power according to the assumed TPC error atterminal 100 can reduce waste power consumption.

In this way, according to the present embodiment, the terminaldetermines the transmission power offset value according to thetransmission condition (in the present embodiment, transmission timeinterval) about the relationship between the uplink channel (uplinksignal) transmitted and the succeeding SRS to be transmitted. With thisconfiguration, the terminal can reduce SRS transmission power as theabove transmission time interval is shorter, i.e. the influence of theTPC error is smaller. This can prevent deterioration of the SINRmeasurement accuracy caused by the TPC error at the base station whilesuppressing an increase in power consumption of the terminal.Furthermore, according to the present embodiment, the terminal canreduce the inter-cell interference by reducing the SRS transmissionpower to a necessary minimum.

Furthermore, in the present embodiment, in the case where, for example,the system defines in advance the correspondence between elapsed time Tand correction value Δ_(offset) shown in FIG. 4, signaling does not needto be performed for every SRS transmission for SRS transmission powercontrol. Alternatively, in the ease where the correspondence betweenelapsed time T and correction value Δ_(offset) shown in FIG. 4 isreported in advance from the base station to a terminal as a parameter,the parameter needs to be reported in a relatively long period or justonce to the terminal and signaling does not need to be performed forevery SRS transmission for SRS transmission power control. Thus, in suchcases, an increase in signaling overhead for the SRS transmission powercontrol can be suppressed.

Furthermore, according to the present embodiment, because the basestation can know the difference between the SRS transmission power andthe PUSCH transmission power (i.e. transmission power offset value forSRS), the base station can derive the SINR measurement value for PUSCH(SINR measurement value for data) from the SINR measurement value of SRS(SINR measurement value for SRS). Thus, prevention of deterioration ofthe SINR measurement accuracy of SRS at the base station as describedabove can lead to prevention of deterioration of the SINR measurementaccuracy of PUSCH. This enables the base station to perform precisescheduling of PUSCH (frequency resource assignment and MCS selection).

In the present embodiment, the case has been described in which theterminal uses elapsed time T between the transmission time of the uplinkchannel and the transmission time of the succeeding SRS (FIG. 4). In thepresent invention, however, the terminal may determine correction valueΔ_(offset) for offset value P_(SRS) _(—) _(OFFSET), which is instructedfrom the base station, according to an elapsed time between thetransmission time of the SRS transmitted from the terminal and thetransmission time of the succeeding SRS to be transmitted (i.e. thetransmission period of SRS). Specifically, as shown in FIG. 5, theterminal may set correction value Δ_(offset) to −6 dB in the ease of SRStransmission period T_(SRS) of 20 ms or less (the TPC error is small),and may set correction value Δ_(offset) to 0 dB in the case of SRStransmission period T_(SRS) longer than 20 ms (the TPC error is large).That is, the terminal determines offset value P_(SRS) _(—) _(OFFSET)such that the SRS transmission power in the case of a shorter SRStransmission period is smaller than the SRS transmission power in thecase of a longer SRS transmission period. In FIG. 5, P_(SRS) _(—)_(OFFSET) shown in Equation 2 is determined with reference to an assumedmaximum TPC error, as with FIG. 4. That is, the terminal sets smallercorrection value Δ_(offset) for shorter SRS transmission period T_(SRS)to reduce the SRS transmission power. In other words, the terminaldetermines correction value Δ_(offset) such that the SRS transmissionpower in the case of shorter SRS transmission period T_(SRS) (T_(SRS)≦20ms in FIG. 5, i.e. the TPC error is small) is smaller than the SRStransmission power in the case of longer SRS transmission period T_(SRS)(T_(SRS)>20 ms in FIG. 5, i.e. the TPC error is large). Here, SRStransmission period T_(SRS) is a parameter reported in advance from thebase station to a terminal. Hence, the base station can determine theoffset value according to the SRS transmission period and thus does notneed to always grasp the transmission times of uplink channels in allterminals (elapsed times T in FIG. 4) unlike the present embodiment.That is, compared to a case described in the present embodiment (whenelapsed time T in FIG. 4 is used), in the case where SRS transmissionperiod T_(SRS) is used for SRS transmission power control, it is easy toshare information for the SRS transmission power control (process ofsetting the transmission power offset value) between the terminal(offset setting section 106 in FIG. 2) and the base station (offsetsetting section 208 in FIG. 3).

Furthermore, periodically-transmitted SRSs are explained in FIG. 5. Thepresent invention, however, may be applied to the SRS to which notransmission period is set (SRS without a transmission period), such asa one-shot SRS. For example, a terminal may treat an SRS without atransmission period as the SRS with a maximum transmission period amongthe transmission periods of the SRSs to which a transmission period isset (e.g. 320 ms in LTE). Alternatively, the terminal may determine thetransmission power offset value for the SRS without a transmissionperiod according to elapsed time T between the transmission time of theuplink channel (PUSCH, PUCCH, or SRS) transmitted and the transmissiontime of the succeeding SRS (such as one-shot SRS), as with the case inFIG. 4.

Furthermore, in the present embodiment, a case has been explained inwhich the terminal selects either of two values as correction valueΔ_(offset) for offset value P_(SRS) _(—) _(OFFSET), which is instructedfrom the base station, according to elapsed time T in FIG. 4 or SRStransmission period T_(SRS) in FIG. 5 (i.e. the case in whichtransmission power offset value (P_(SRS) _(—) _(OFFSET)+Δ_(offset))shown in Equation 2 may take two values.) Alternatively, the terminalmay select one of three or more values as correction value Δ_(offset)for offset value P_(SRS) _(—) _(OFFSET), which is instructed from thebase station, according to elapsed time T or SRS transmission periodT_(SRS) (i.e. transmission power offset value (P_(SRS) _(—)_(OFFSET)+Δ_(offset)) shown in Equation 2 may take three or morevalues).

Furthermore, in the present embodiment, a case has been explained inwhich the terminal changes correction value Δ_(offset) for offset valueP_(SRS) _(—) _(OFFSET) instructed from the base station according toelapsed time T or SRS transmission period T_(SRS) as shown in FIG. 4 or5. Alternatively, the terminal may change the equations for determiningthe SRS transmission power according to elapsed time T or SRStransmission period T_(SRS). For example, the terminal calculates SRStransmission power P_(SRS) (i) in accordance with the following Equation4 if elapsed time T is 20 ms or less, and calculates SRS transmissionpower P_(SRS)(i) in accordance with the following Equation 5 if elapsedtime T is longer than 20 ms.

[3]P _(SRS)(i)=min{P _(CMAX),(P _(SRS) _(—) _(OFFSET)+Δ_(offset))+10log₁₀(M _(SRS))+P _(O) _(—) _(PUSCH)(j)+α(j)·PL+f(i)}  (Equation 4)[4]P _(SRS)(i)=min{P _(CMAX) ,P _(SRS) _(—) _(OFFSET)+10 log₁₀(M _(SRS))+P_(O) _(—) _(PUSCH)(j)+α(j)·PL+f(i)}  (Equation 5)

In Equations 4 and 5, P_(SRS) _(—) _(OFFSET) is set as a value that canprevent deterioration of the SINR measurement accuracy even if a maximumTPC error occurs which is expected in the case of longer elapsed time Tthan 20 ms. That is, if elapsed time T is longer than 20 ms (the TPCerror is large), the terminal calculates SRS transmission powerP_(SRS)(i) without correcting offset value P_(SRS) _(—) _(OFFSET) asshown in Equation 5. On the other hand, if elapsed time T is 20 ms orless (the TPC error is small), the terminal uses correction valueΔ_(offset) to correct offset value P_(SRS) _(—) _(OFFSET), andcalculates SRS transmission power P_(SRS)(i), as shown in Equation 4.With this configuration, as with the present embodiment, powerconsumption of the terminal can be reduced while deterioration of theSINR measurement accuracy of SRS is prevented.

Embodiment 2

In Embodiment 1, a case has been described in which a terminaldetermines a correction value for an offset value instructed from a basestation according to the transmission time interval (elapsed time)between the uplink channel transmitted and the succeeding SRS to betransmitted. In the present embodiment, a case will be described inwhich the terminal determines the correction value for the offset valueinstructed from the base station according to the difference intransmission power between the uplink channel transmitted and thesucceeding SRS to be transmitted.

The present embodiment will now be described in detail. FIG. 6 shows aconfiguration of terminal 300 according to the present embodiment.Components in FIG. 6 that are the same as components in Embodiment 1(FIG. 2) will be assigned the same reference numerals as in FIG. 2 andoverlapping explanations will be omitted.

In terminal 300 in FIG. 6, offset setting section 301 includes powerdifference calculation section 302 and offset value determinationsection 303. Offset setting section 301 determines an offset value forPUSCH transmission power (transmission power offset value. (P_(SRS) _(—)_(OFFSET)+Δ_(offset)) shown in Equation 2) which is used to determinetransmission power of the RS sequence (SRS).

Specifically, power difference calculation section 302 calculates powerdifference ΔP (scale of relative power tolerance), which is thedifference between the transmission power of the uplink channeltransmitted from terminal 300 (e.g. an uplink signal including a PUSCH,a PUCCH and an SRS) and the transmission power of the succeeding SRS tobe transmitted from terminal 300. Power difference calculation section302 uses transmission power calculated by using uncorrected offset valueP_(SRS) _(—) _(OFFSET) instructed from base station 200 (FIG. 3), as thetransmission power of the succeeding SRS to be transmitted. Then, powerdifference calculation section 302 outputs the calculated powerdifference ΔP to offset value determination section 303.

Offset value determination section 303 determines correction valueΔ_(offset) for offset value P_(SRS) _(—) _(OFFSET) instructed from basestation 200 according to power difference ΔP from power differencecalculation section 302. Then, offset value determination section 303uses the determined correction value Δ_(offset) to correct offset valueP_(SRS) _(—) _(OFFSET) instructed from base station 200, therebydetermining transmission power offset value ((P_(SRS) _(—)_(OFFSET)+Δ_(offset)) shown in Equation 2). Then, offset valuedetermination section 303 outputs the determined offset value (P_(SRS)_(—) _(OFFSET)+Δ_(offset)) for the PUSCH transmission power totransmission power control section 111.

Furthermore, offset setting section 208 (FIG. 3) of base station 200according to the present embodiment performs the same process as offsetsetting section 301 of terminal 300. That is, offset setting section 208determines the offset value for the PUSCH transmission power(transmission power offset value. i.e. (P_(SRS) _(—)_(OFFSET)+Δ_(offset)) shown in Equation 2), which is used to determinethe transmission power of an SRS to be transmitted from terminal 300(desired terminal). That is, offset setting section 208 determinescorrection value Δ_(offset) for offset value P_(SRS) _(—) _(OFFSET)according to power difference ΔP, which is the difference between thetransmission power of the uplink channel transmitted from a desiredterminal and the transmission power of the succeeding SRS to betransmitted from the desired terminal (transmission power calculated byusing uncorrected offset value P_(SRS) _(—) _(OFFSET)), and determinestransmission power offset value (P_(SRS) _(—) _(OFFSET)+Δ_(offset)).

Next, the process of setting the transmission power offset value inoffset setting section 301 of terminal 300 (FIG. 6) will be explained indetail.

Here, in the case where an amplifier circuit having a plurality of poweramplifiers (PAs) is employed in terminal 300, the number of PAs used foramplification varies more significantly as the power difference, whichis the difference between the transmission power of the uplink channeltransmitted (a PUSCH, a PUCCH, or an SRS) and the transmission power ofthe succeeding uplink to be transmitted, increases. That is, since thenumber of PAs used for amplification varies more significantly as thepower difference between uplink channels increases, errors in the PAsare added up after the power difference is caused, increasing the TPCerror.

Furthermore, transmission power is proportional to the frequencybandwidth of a transmission signal. For this reason, the frequencyposition and bandwidth of a transmission signal varies moresignificantly as the power difference increases (as the transmissionpower increases or decreases more significantly). Furthermore, becausethe amplification characteristics of the PA also depends on thefrequency (frequency position and bandwidth), the TPC error increases asthe power difference increases (as the frequency position and bandwidthvaries more significantly).

That is, at terminal 300, the TPC error varies depending on the powerdifference between the transmission power of the uplink channeltransmitted and the transmission power of the succeeding uplink channelto be transmitted. Specifically, the TPC error is assumed to decrease asthe power difference decreases (as the number of PAs varies lesssignificantly, i.e. the frequency position and bandwidth of thetransmission signal varies less significantly).

In view of the above, offset setting section 301 determines thetransmission power offset value ((P_(SRS) _(—) _(OFFSET)+Δ_(offset))shown in Equation 2) according to power difference ΔP, which is thedifference between the transmission power of the uplink channeltransmitted and the transmission power of the SRS that is calculatedusing offset value P_(SRS) _(—) _(OFFSET) (the transmission power of thesucceeding SRS to be transmitted). The transmission power offset valueis used to determine the SRS transmission power.

In the following explanation, as with Embodiment 1, terminal 300 usesthe equation of transmission power shown in Equation 2 to calculate SRStransmission power P_(SRS)(i). P_(SRS) _(—) _(OFFSET) shown in Equation2 is determined with reference to an assumed maximum TPC error as withEmbodiment 1. Furthermore, P_(SRS) _(—) _(OFFSET) shown in Equation 2 isreported from base station 200 to terminal 300, as with Embodiment 1.

Power difference calculation section 302 in offset setting section 301calculates power difference ΔP, which is the difference between thetransmission power of the uplink channel transmitted and thetransmission power calculated using offset value P_(SRS) _(—) _(OFFSET)(the transmission power of the succeeding SRS to be transmitted that iscalculated using uncorrected offset value).

Then, offset value determination section 303 in offset setting section301 determines correction value Δ_(offset) for offset value P_(SRS) _(—)_(OFFSET) instructed from base station 200 according to power differenceΔP calculated in power difference calculation section 302.

For example, as shown in FIG. 7, offset value determination section 303determines correction value Δ_(offset) as follows: 0 dB is associatedwith power difference ΔP of 15 dB or greater, −1 dB is associated withpower difference ΔP of 10 dB or greater and less than 15 dB, −3 dB isassociated with power difference ΔP of 4 dB or greater and less than 10dB, −4 dB is associated with power difference ΔP of 3 dB or greater andless than 4 dB, −5 dB is associated with power difference ΔP of 2 dB orgreater and less than 3 dB, and −6 dB is associated with powerdifference ΔP of less than 2 dB. Then, offset value determinationsection 303 adds above-determined correction value Δ_(offset) to offsetvalue P_(SRS) _(—) _(OFFSET) instructed from base station 200 todetermine transmission power offset value (P_(SRS) _(—)_(OFFSET)+Δ_(offset)).

That is, in the case where offset value P_(SRS) _(—) _(OFFSET)instructed from base station 200 is determined with reference to anassumed maximum TPC error, offset value determination section 303 setssmaller correction value Δ_(offset) for smaller power difference ΔP(smaller TPC error). That is, offset value determination section 303corrects offset value P_(SRS) _(—) _(OFFSET) into a smaller value forsmaller power difference ΔP, and sets the smaller value than offsetvalue P_(SRS) _(—) _(OFFSET) as the transmission power offset value.

As described above, terminal 300 sets a different correction value forthe offset value instructed from base station 200 according to thedifference in the transmission power (power difference ΔP) between theuplink channel transmitted from terminal 300 and the succeeding SRS tobe transmitted from the terminal 300. Specifically, terminal 300determines correction value Δ_(offset) such that SRS transmission powerP_(SRS)(i) in the case of smaller power difference ΔP (i.e. the TPCerror is small) is smaller than SRS transmission power P_(SRS)(i) in thecase of greater power difference ΔP (i.e. the TPC error is large). Thatis, terminal 300 sets smaller SRS transmission power for smaller powerdifference ΔP.

As described above, the TPC error decreases as power difference ΔPdecreases. For this reason, when terminal 300 sets smaller SRStransmission power for smaller power difference ΔP, there is a lowprobability that the reception SINR decreases to a certain level (0 dBor less in FIG. 1) due to the influence of the TPC error. Thus, the SINRmeasurement accuracy at base station 200 is less likely to bedeteriorated.

That is, terminal 300 can set the SRS transmission power down to anecessary minimum value with which a desired reception SINR can beacquired at base station 200 by correcting the offset value instructedfrom base station 200 according to power difference ΔP. Here, thedesired reception SINR refers to reception SINR with which the SINRmeasurement accuracy is not deteriorated. With this configuration, theSINR measurement accuracy of SRS (measurement accuracy of channelquality) at base station 200 can be ensured while power consumption atterminal 300 is reduced to a necessary minimum. In other words,determination of appropriate SRS transmission power according to theassumed TPC error at terminal 300 can reduce waste power consumption.

In this way, according to the present embodiment, the terminaldetermines the transmission power offset value according to thetransmission condition (in the present embodiment, difference oftransmission power) about the relationship between the uplink channel(uplink signal) transmitted and the succeeding SRS to be transmitted.With this configuration, the terminal can reduce SRS transmission poweras the above difference of transmission power is smaller, i.e. as theinfluence of the TPC error is smaller. This can prevent deterioration ofthe SINR measurement accuracy caused by the TPC error at the basestation while suppressing an increase in power consumption of theterminal. Furthermore, according to the present embodiment, the terminalcan reduce the inter-cell interference by reducing the SRS transmissionpower to a necessary minimum.

Furthermore, in the present embodiment, in the case where, for example,the system defines in advance the correspondence between powerdifference ΔP and correction value Δ_(offset) shown in FIG. 7, signalingdoes not need to be performed for every SRS transmission for SRStransmission power control. Alternatively, in the ease where thecorrespondence between power difference ΔP and correction valueΔ_(offset) shown in FIG. 7 is reported in advance from the base stationto the terminal as a parameter, the parameter needs to be reported in arelatively long period or just once to the terminal and signaling doesnot need to be performed for every SRS transmission for SRS transmissionpower control. Thus, in such cases, an increase in signaling overheadfor the SRS transmission power control can be suppressed as withEmbodiment 1.

Furthermore, according to the present embodiment, because the basestation can know the difference between the SRS transmission power andthe PUSCH transmission power (i.e. transmission power offset value forSRS), the base station can derive the SINR measurement value for PUSCH(SINR measurement value for data) from the SINR measurement value of SRS(SINR measurement value for SRS). Thus, prevention of deterioration ofthe SINR measurement accuracy of SRS at the base station as describedabove leads to prevention of deterioration of the SINR measurementaccuracy of PUSCH. This enables the base station to perform precisescheduling of PUSCH (frequency resource assignment and MCS selection) aswith Embodiment 1.

Embodiment 3

In Embodiment 1, a case has been described in which a terminaldetermines a correction value for an offset value instructed from a basestation according to the SRS transmission period. In the presentembodiment, a ease will be described in which the terminal sets theoffset value instructed from the base station to an SRS to which notransmission period is set.

The present embodiment will now be described in detail. FIG. 8 shows aconfiguration of terminal 500 according to the present embodiment.Components in FIG. 8 that are the same as components in Embodiment 1(FIG. 2) will be assigned the same reference numerals as in FIG. 2 andoverlapping explanations will be omitted.

In terminal 500 in FIG. 8, offset setting section 501 includes SRS-typedetermination section 502 and offset value determination section 503.Offset setting section 501 determines an offset value for PUSCHtransmission power (transmission power offset value. P_(SRS) _(—)_(OFFSET) shown in Equation 1) which is used to determine transmissionpower of an RS sequence (SRS).

Specifically, SRS-type determination section 502 determines the type ofthe succeeding SRS to be transmitted in an uplink from terminal 500. Thetypes of SRS include an SRS to which a transmission period is set(hereinafter referred to as “periodic-SRS”) and an SRS to which notransmission period is set (hereinafter referred to as “aperiodic-SRS”).The aperiodic-SRS refers to an SRS transmitted from a terminal once orpredetermined times after the terminal receives a trigger signal frombase station 200. SRS-type determination section 502 outputs informationindicating which type the succeeding SRS to be transmitted belongs to(type of the succeeding SRS to be transmitted) to offset valuedetermination section 503.

Offset value determination section 503 selects offset value P_(SRS) _(—)_(OFFSET) (P_(SRS) _(—) _(OFFSET) shown in Equation 1), which isassociated with the type of SRS, according to the type of SRS receivedfrom SRS-type determination section 502, the offset value P_(SRS) _(—)_(OFFSET) being instructed in advance from base station 200. Then,offset value determination section 503 outputs the selected offset value(P_(SRS) _(—) _(OFFSET)) for PUSCH transmission power to transmissionpower control section 111.

Furthermore, offset setting section 208 (FIG. 3) of base station 200according to the present embodiment performs the same process as offsetsetting section 501 of terminal 500. That is, offset setting section 208determines the offset value for the PUSCH transmission power(transmission power offset value. i.e. P_(SRS) _(—) _(OFFSET) shown inEquation 1), which is used to determine the transmission power of an SRSto be transmitted from terminal 500 (desired terminal). That is, offsetsetting section 208 selects offset value P_(SRS) _(—) _(OFFSET)associated with the type of SRS according to the type of the succeedingSRS to be transmitted from the desired terminal.

Next, the process of setting the transmission power offset value inoffset setting section 501 of terminal 500 (FIG. 8) will now beexplained in detail.

The aperiodic-SRS and periodic-SRS need different transmission power.Specifically, the aperiodic-SRS tends to need greater transmission powerthan the periodic-SRS for the following three reasons:

First, with the aperiodic-SRS, an elapsed time between transmissions islikely to be longer than that for the periodic-SRS to be transmittedperiodically, and thus the TPC error is likely to increase. Setting ashorter transmission period (e.g. 20 ms or less) to the periodic-SRSreduces the TPC error. On the other hand, in the case where the terminaldoes not transmit an uplink channel (e.g. PUSCH) for some time beforetransmission of the aperiodic-SRS, the elapsed time of the transmissionsis long, increasing the TPC error. In order to prevent deterioration ofthe measurement accuracy of channel quality caused by the TPC error,greater transmission power must be assigned to the aperiodic-SRS.

Second, because the number of aperiodic-SRSs to be transmitted islimited compared to that of periodic-SRSs, the measurement accuracycannot be improved by averaging a plurality of aperiodic-SRSs unlike thecase with the periodic-SRS. Hence, greater transmission power must beassigned to the aperiodic-SRS to acquire the measurement accuracyequivalent to that of the periodic-SRS.

Lastly, the aperiodic-SRS may be used to instantaneously measure theuplink quality to precisely select MCS for the PUSCH. That is, theprecise measurement accuracy is required for the aperiodic-SRS, and thusgreater transmission power must be assigned to the aperiodic-SRS thanthe periodic-SRS.

For these reasons, necessary transmission power may vary depending onthe type of SRS (aperiodic-SRS or periodic-SRS). If offset value P_(SRS)_(—) _(OFFSET) used to determine the SRS transmission power is constantregardless of the type of SRS, the terminal must set the transmissionpower (offset value) of the type of SRS requiring greater transmissionpower (here, mainly, aperiodic-SRS) to the transmission power of alltypes of SRS including other types of SRS (here, mainly, periodic-SRS).In this case, greater transmission power than necessary is assigned tothe periodic-SRS, increasing power consumption of the terminal.Furthermore, if offset value P_(SRS) _(—) _(OFFSET) is updated at everytransmission of the aperiodic-SRS, the frequency of reporting of controlinformation increases, increasing the system overhead.

In the present embodiment, to overcome the above problem, offset settingsection 501 of terminal 500 determines offset value P_(SRS) _(—)_(OFFSET) (P_(SRS) _(—) _(OFFSET) shown in Equation 1), which is used todetermine the SRS transmission power, according to the type ofsucceeding SRS to be transmitted (specifically, aperiodic-SRS andperiodic-SRS).

In the following explanation, terminal 500 uses the equation oftransmission power shown in Equation 1 to calculate SRS transmissionpower P_(SRS)(i). Furthermore, P_(SRS) _(—) _(OFFSET) shown in Equation1 is determined with reference to, for example, a maximum TPC error ofeach type of SRS. That is, offset value P_(SRS) _(—) _(OFFSET) is set toa necessary value for meeting the requirements for measurement quality.Offset value P_(SRS) _(—) _(OFFSET) is reported in advance from basestation 200 to terminal 400 (the method of reporting P_(SRS) _(—)_(OFFSET) of each type of SRS will be explained in detail later).

SRS-type determination section 502 outputs the determined type ofsucceeding SRS to be transmitted (aperiodic-SRS or periodic-SRS) tooffset value determination section 503.

Then, offset value determination section 503 selects offset valueP_(SRS) _(—) _(OFFSET) associated with the type of SRS determined inSRS-type determination section 502.

For example, as shown in FIG. 9, offset value determination section 503sets offset value P_(SRS) _(—) _(OFFSET) to 3 dB when the terminaltransmits the aperiodic-SRS, and sets offset value P_(SRS) _(—)_(OFFSET) to 0 dB when the terminal transmits the periodic-SRS. That is,offset value determination section 503 sets a greater offset value forthe transmission power of the aperiodic-SRS, which requires greatertransmission power, than the offset value for the transmission power ofthe periodic-SRS, as described above.

That is, offset value determination section 503 determines the offsetvalue according to whether the transmission period is set to the SRS.Specifically, offset value determination section 503 sets the offsetvalue such that the transmission power of the periodic-SRS is lower thanthe transmission power of the aperiodic-SRS.

Here, the correspondence between the type of SRS and offset valueP_(SRS) _(—) _(OFFSET) shown in FIG. 9 is reported in advance from basestation 200 to terminal 500. An optimum offset value P_(SRS) _(—)_(OFFSET) of each type of SRS is determined according to the conditionfor determining an SRS at base station 200 (e.g. the transmission periodof periodic-SRS or the transmission timing of aperiodic-SRS). Hence, theabove correspondence does not need to be reported frequently (in a shortperiod).

Here, the specific methods of reporting the correspondence between thetype of SRS and the offset value shown in FIG. 9 from base station 200to terminal 500 will now be explained. In LTE, offset value P_(SRS) _(—)_(OFFSET) of the periodic-SRS is reported as information about powercontrol (e.g. “UplinkPowerControl” prescribed in [3GPP TS36.331V8.9.0(2010-03), “3GPP TSGRAN E-UTRA RRC Protocol specification (Release8)”]. Information containing P_(o) _(—) _(PUSCH) or α, which areparameters in Equation 1).

On the other hand, for reporting offset value P_(SRS) _(—) _(OFFSET) ofthe aperiodic-SRS in addition to offset value P_(SRS) _(—) _(OFFSET) ofthe periodic-SRS, as performed in the present embodiment, the followingfour methods may be employed. As explained below, some reporting methodscan reduce signaling for reporting offset value P_(SRS) _(—) _(OFFSET)of the aperiodic-SRS.

The first reporting method is a method of reporting offset value P_(SRS)_(—) _(OFFSET) of the aperiodic-SRS by containing the offset value ininformation about power control, as with the method of reporting offsetvalue P_(SRS) _(—) _(OFFSET) of the periodic-SRS. In this reportingmethod, in order to allow terminal 500 to transmit an aperiodic-SRS,base station 200 must also report SRS resource information foraperiodic-SRS in addition to the information about power control.Examples of the SRS resource information includes information indicatingSRS transmission resource, such as “SoundingRS-UL-Config” prescribed in[3GPP TS36.331 V8.9.0(2010-03), “3GPP TSGRAN E-UTRA RRC Protocolspecification (Release 8)”] (information containing, for example, thebandwidth or frequency hopping pattern for SRS transmission). Thus, inthis reporting method, the base station must report two kinds ofparameters to allow the terminal to transmit the aperiodic-SRS,increasing the signaling load.

The second reporting method is a method of reporting offset valueP_(SRS) _(—) _(OFFSET) of the aperiodic-SRS separately by containing theoffset value in the SRS resource information for the aperiodic-SRS. Inthis reporting method, in order to allow terminal 500 to transmit theaperiodic-SRS, base station 200 needs to report only the SRS resourceinformation for the aperiodic-SRS. Thus, this reporting method requiresless signaling load for reporting offset value P_(SRS) _(—) _(OFFSET) ofthe aperiodic-SRS than the first reporting method.

The third reporting method is a method of reporting correction value(Δ_(offset)) for offset value P_(SRS) _(—) _(OFFSET) of the periodic-SRSas with Embodiments 1 and 2. The transmission powers of the periodic-SRSand aperiodic-SRS are calculated using Equations 1 and 2, respectively.Here, because the range of Δ_(offset) to be reported does not need to beset greater than the range of P_(SRS) _(—) _(OFFSET) to be reported, thesmaller number of reporting bits can be used for Δ_(offset) than P_(SRS)_(—) _(OFFSET), which requires four bits in LTE. Hence, this reportingmethod requires less signaling load for reporting offset value P_(SRS)_(—) _(OFFSET) of the aperiodic-SRS (i.e. “P_(SRS) _(—)_(OFFSET)+Δ_(offset)” shown in Equation 2). Correction value Δ_(offset)may be defined as a fixed value for the whole system. In this case,signaling from base station 200 to terminal 500 does not need to beperformed.

The fourth reporting method is a method of reporting offset valueP_(SRS) _(—) _(OFFSET) in a different range for the aperiodic-SRS fromthat for the periodic-SRS. For example, base station 200 uses adifferent range of offset value P_(SRS) _(—) _(OFFSET) for theaperiodic-SRS from that for the periodic-SRS, even when the same numberof reporting bits is used for the both two types of SRS:

Range of offset value P_(SRS) _(—) _(OFFSET) of aperiodic-SRS to bereported: −7.5 to 15 dB

Range of offset value P_(SRS) _(—) _(OFFSET) of periodic-SRS to bereported: −10.5 to 12 dB

That is, the range of offset value P_(SRS) _(—) _(OFFSET) of theperiodic-SRS to be reported is shifted to the positive direction by acertain amount (by 3 dB in the above example) to determine the range ofoffset value P_(SRS) _(—) _(OFFSET) of the aperiodic-SRS to be reported.Thus, in this reporting method, necessary transmission power can bedetermined according to the type of SRS without increasing the number ofsignaling bits.

In this way, in the present embodiment, terminal 500 determines thetransmission power offset value for SRS according to the type ofsucceeding SRS to be transmitted from terminal 500. This enablesterminal 500 to assign individual necessary transmission power to theaperiodic-SRS and the periodic-SRS. Furthermore, according to thepresent embodiment, at terminal 500, the transmission power identical tothat of the aperiodic-SRS does not need to be assigned to theperiodic-SRS, and thus the transmission power of the periodic-SRS doesnot increase. For this reason, the periodic-SRS can be transmitted witha necessary minimum power. Thus, it is possible to prevent the greatertransmission power than necessary from being assigned to theperiodic-SRS, reducing the power consumption of the terminal. Thus,according to the present embodiment, deterioration of the SINRmeasurement accuracy caused by the TPC error can be prevented at basestation 200 while an increase in power consumption of terminal 500 isreduced. Furthermore, according to the present embodiment, offset valueP_(SRS) _(—) _(OFFSET) does not need to be updated at every transmissionof the aperiodic-SRS, preventing an increase in the system overhead.

Furthermore, in the present embodiment, a case has been described wherethe two types of SRS, the aperiodic-SRS and periodic-SRS, are used.SRSs, however, may be categorized into a greater number of types. Forexample, in LTE-Advanced, the use of “one-shot SRS” and “multi-shot SRS”as the aperiodic-SRS is being studied. The one-shot SRS is transmittedonly once after reception of a trigger signal from a base station andthe multi-shot SRS is transmitted predetermined multiple times onlyafter reception of the trigger signal from the base station. Examples ofthe trigger signal from the base station include a signal containinginformation constituting at least one bit, which is transmitted througha downlink control channel called a physical downlink control channel(PDCCH). The base station uses this information to instruct a terminalto transmit the aperiodic-SRS. In response to the trigger signal fromthe base station, the terminal transmits an SRS once or predeterminedmultiple times during a predetermined SRS transmission time.Furthermore, the multi-shot SRSs can be categorized into an SRStransmitted in a single frequency band for the purpose of improving themeasurement accuracy of the channel quality and an SRS transmitted indifferent frequency bands for the purpose of measuring the channelquality in a wide band. The terminal may define these aperiodic-SRSs asdifferent types of SRS to determine offset value P_(SRS) _(—) _(OFFSET)according to the type of SRS.

For example, as shown in FIG. 10, a terminal (offset value determinationsection 503) sets offset value P_(SRS) _(—) _(OFFSET) of 3 dB to anone-shot SRS, sets offset value P_(SRS) _(—) _(OFFSET) of 1.5 dB to amulti-shot SRS transmitted in a single frequency band, and sets offsetvalue P_(SRS) _(—) _(OFFSET) of 3 dB to the multi-shot SRS transmittedin different frequency bands. That is, as shown in FIG. 10, the terminalassociates greater offset value P_(SRS) _(—) _(OFFSET) with the one-shotSRS than with the multi-shot SRS transmitted in a single frequency bandfor the following reason: in the case of the multi-shot SRS transmittedin a single band, averaging a plurality of SRSs at the base station canimprove the measurement quality of the channel. On the other hand, inthe case of the one-shot SRS, the improvement of the measurement qualityby virtue of averaging of SRSs cannot be expected at the base station,and thus the one-shot SRS requires greater transmission power.Furthermore, the terminal sets the same offset value P_(SRS) _(—)_(OFFSET) to the multi-shot SRS transmitted in different frequency bandsand the one-shot SRS for the following reason: in the ease of themulti-shot SRS transmitted in different frequency bands, the improvementof the measurement quality by virtue of averaging of SRSs cannot beexpected at the base station, as with the case of the one-shot SRS.Thus, the multi-shot SRS requires the same necessary transmission poweras the one-shot SRS.

Alternatively, the terminal may categorize the aperiodic-SRSs intodifferent types of SRS depending on the interval of subcarriers in whichthe aperiodic-SRS is arranged, and may determine offset value P SRS _(—)_(OFFSET) according to the type of SRS.

For example, as shown in FIG. 11, the terminal (offset valuedetermination section 503) sets offset value P_(SRS) _(—) _(OFFSET) of1.5 dB to an aperiodic-SRS arranged at a subcarrier interval of 15 kHz,and sets offset value P_(SRS) _(—) _(OFFSET) of 3.0 dB to anaperiodic-SRS arranged at a subcarrier interval of 30 kHz. That is, theterminal associates greater offset value P_(SRS) _(—) _(OFFSET) With anaperiodic-SRS arranged at a longer subcarrier interval. This is becauseextension of the subcarrier interval leads to a decrease in the averagenumber of subcarriers used for the measurement of channel quality perunit frequency band, thus impairing the measurement accuracy of thechannel quality (making variation greater) at the base station. Thus,the aperiodic-SRS arranged at a longer subcarrier interval requiresgreater transmission power.

Embodiments of the present invention have been described.

In the present invention, configurations of Embodiments 1 and 2 may becombined. Specifically, the offset setting section of the terminalincludes the elapsed-time calculation section, the power differencecalculation section, and the offset value determination section, asshown in FIG. 12. That is, the offset value determination section shownin FIG. 12 determines correction value Δ_(offset) for offset valueP_(SRS) _(—) _(OFFSET) shown in Equation 2 according to both of elapsedtime T explained in Embodiment 1 and power difference ΔP explained inEmbodiment 2. Specifically, as shown in FIG. 13, correction valueΔ_(offset) is associated with elapsed time T and power difference ΔP.Correction value Δ_(offset) in FIG. 13 is associated with elapsed time Tand power difference ΔP according to the allowable ranges of the TPCerror prescribed in LTE (for example, see 3GPP TS36.101 v8.9.0 (Table6.3.5.2.1-1)), which are shown in FIGS. 14A and 14B. Here, FIG. 14Ashows the provision of the allowable range of the TPC error (±9.0 dB) inthe case of elapsed time T longer than 20 ms (T>20 ms). FIG. 14B showsthe provision of the allowable range of the TPC error in the case ofelapsed time T of 20 ms or less (T≦20 ms). In FIG. 14B, greater powerdifference ΔP is associated with the greater allowable range of the TPCerror.

In FIG. 13, constant correction value Δ_(offset) (0 dB) is associatedboth with the case of elapsed time of T>20 ms and with the case ofelapsed time of T≦20 ms and ΔP of 15 dB or greater, based on FIGS. 14Aand 14B. That is, constant correction value Δ_(offset) is associatedwith different elapsed times T. Alternatively, according to the presentinvention, greater correction value Δ_(offset) may be associated withlonger elapsed time T as shown in FIG. 15 instead of FIG. 13. That is,in FIG. 15, different correction value Δ_(offset) is associated withdifferent elapsed times T and with different power differences ΔP.Furthermore, in FIG. 13, constant correction value Δ_(offset) isassociated with longer elapsed time T (T>20 ms) regardless of the valueof power difference ΔP. Alternatively, as shown in FIG. 15, differentcorrection value Δ_(offset) may be associated with longer elapsed time T(T>20 ms) according to power difference ΔP.

By using the correspondences in FIGS. 13 and 15, the terminal cancontrol the SRS transmission power by taking into consideration bothelapsed time T and power difference ΔP. That is, the terminal cancontrol SRS transmission power more precisely and can further reduce thewaste power consumption compared to the above embodiments whilepreventing deterioration of the SINR measurement accuracy caused by theTPC error at the base station.

Although a case has been described where a terminal has a single antennain the above embodiments, the present invention can be applied to a casewhere a terminal has a plurality of antennas. For example, as shown inFIG. 16, terminal 400 having N antennas 113-1 to 113-N includestransmission processing sections 401-1 to 401-N corresponding to therespective antennas. Here, each transmission processing section 401includes, for example, components from RS generation section 101 to CPaddition section 105 shown in FIG. 2. Furthermore, offset settingsections 402-1 to 402-N shown in FIG. 16 may employ the sameconfiguration as offset setting section 106 (FIG. 2), offset settingsection 301 (FIG. 6), offset setting section 501 (FIG. 8), or offsetsetting section (FIG. 12). Offset setting sections 402 of respectivetransmission processing sections 401 of terminal 400 shown in FIG. 16determine correction values Δ_(offset) for offset values P_(SRS) _(—)_(OFFSET) (or offset values P_(SRS) _(—) _(OFFSET)) of respective SRSstransmitted from the respective antennas according to the respectivetransmission time intervals (above-described elapsed times T or SRStransmission periods T_(SRS)) or respective differences of transmissionpower (above-described power differences ΔP) in the antennas. Then,transmission power control sections 111 in transmission sections 109 ofterminal 400 control respective transmission power of the SRSstransmitted from the antennas by adding respective correction valuesΔ_(offset) assigned to SRSs transmitted from antennas to respectiveoffset values P_(SRS) _(—) _(OFFSET) (or by using determined offsetvalues P_(SRS) _(—) _(OFFSET)). In this way, terminal 400 separatelydetermines correction values Δ_(offset) (or offset values P_(SRS) _(—)_(OFFSET), for example) which are used to control transmission power ofthe SRSs transmitted from antennas. That is, terminal 400 determinesoffset values for the respective SRSs transmitted from the respectiveantennas according to the respective transmission time intervals betweenSRSs (e.g. SRS transmission periods) in the antennas, and uses theoffset values assigned to respective SRSs to control transmission powerof SRSs transmitted from the antennas. This enables terminal 400 to setdifferent transmission power to each antenna using, for example, acommon parameter (e.g. offset value P_(SRS) _(—) _(OFFSET)) reportedfrom the base station to the antennas. With this configuration, terminal400 can appropriately control the SRS transmission power for eachantenna, and thus can further reduce the SRS transmission power comparedto a conventional technique in which the SRS transmission power iscontrolled uniformly for all antennas.

Furthermore, in the present invention, when a terminal has a pluralityof antennas as explained in FIG. 16, the terminal may controltransmission power of the SRSs by using the ratio of each correctionvalue Δ_(offset) for offset value P_(SRS) _(—) _(OFFSET) (or ratio ofeach offset value P_(SRS) _(—) _(OFFSET)) assigned to each SRS, as theratio of the transmission power assigned to each SRS to the totaltransmission power assigned to all SRSs transmitted from the antennas.Specifically, although the above embodiments describes a case in whichtransmission power of an SRS transmitted from each antenna is defined asP_(SRS)(i) shown in Equation 1 or 2, this embodiment describes a case inwhich the terminal defines the total transmission power of a pluralityof SRSs transmitted simultaneously from the plurality of antennas asP_(SRS)(i) shown in Equation 1 or 2. That is, total transmission powerP_(SRS)(i) of the plurality of SRSs is calculated by adding offset valueP_(SRS) _(—) _(OFFSET) to the PUSCH transmission power. Then, as withthe above embodiments, the terminal determines correction valuesΔ_(offset) for respective offset values P_(SRS) _(—) _(OFFSET) accordingto the respective transmission time intervals (elapsed times T (e.g.FIG. 4)) or power differences ΔP (e.g. FIG. 7)), or differences oftransmission power (power differences ΔP (e.g. FIG. 7)) in therespective antennas (or offset values P_(SRS) _(—) _(OFFSET) isdetermined according to the respective SRS transmission periods (typesof SRS (e.g. FIGS. 9-11) in the antennas). Then, the terminal controlstransmission power of the SRSs by using the ratio of correction valueΔ_(offset) (or the ratio of offset value P_(SRS) _(—) _(OFFSET))assigned to each of the SRSs transmitted from the respective antennas asthe ratio of transmission power assigned to each of the SRS transmittedfrom the respective antennas to the total transmission power P_(SRS)(i).That is, in an antenna from which an SRS having smaller correction valueΔ_(offset) (or offset value P_(SRS) _(—) _(OFFSET)) is transmitted, theratio of transmission power of the SRS to total transmission powerP_(SRS) (i) is smaller and smaller transmission power is assigned to theantenna. In other word, in the antenna from which an SRS having smallercorrection value Δ_(offset) is transmitted (the TPC error is smaller),deterioration of the SINR measurement accuracy at the base station canbe further prevented and the SRS transmission power at the terminal canbe further reduced. In this way, similar effects to the aboveembodiments can be obtained even in the case where the terminal usescorrection value Δ_(offset) determined according to elapsed time T orpower difference ΔP (or the SRS transmission period (offset valueP_(SRS) _(—) _(OFFSET) determined according to the type of SRS)), as theratio of transmission power of each SRS transmitted from each antenna.

Furthermore, in the above embodiments, a case has been described whereP_(SRS) _(—) _(OFFSET) shown in Equation 2 is determined with referenceto an assumed maximum TPC error (e.g. FIGS. 4 and 7). Alternatively,according to the present invention, P_(SRS) _(—) _(OFFSET) shown inEquation 2 may be determined with reference to an assumed minimum TPCerror. In this case, correction value Δ_(offset) may be determined suchthat greater correction value Δ_(offset) is associated with longerelapsed time T (T>20 ms) as shown in FIG. 17, and such that greatercorrection value Δ_(offset) is associated with greater power differenceΔP as shown in FIG. 18.

Although a case has been described with the above embodiment where thepresent invention is configured as an antenna, the present invention isalso applicable to an antenna port.

The term, antenna port, refers to a logical antenna configured with oneor a plurality of physical antennas. That is, an antenna port does notalways refer to one physical antenna, and can also refer to, forexample, an array antenna configured with a plurality of antennas.

For example, in LTE, how many physical antennas constitute the antennaport is not prescribed, and an antenna port is prescribed as a minimumunit by which a base station can transmit a different reference signal.

Further, an antenna port is also prescribed as a minimum unit with whichthe weight of precoding vector is multiplied.

Also, although cases have been described with the above embodiment asexamples where the present invention is configured by hardware, thepresent invention can also be realized by software.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of a programmableFPGA (Field Programmable Gate Array) or a reconfigurable processor whereconnections and settings of circuit cells within an LSI can bereconfigured is also possible.

Further, if integrated circuit technology conies out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosures of Japanese Patent Application No. 2010-105323, filed onApr. 30, 2010 and Japanese Patent Application No. 2010-249128, filed onNov. 5, 2010, including the specifications, drawings and abstracts, areincorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a mobile communication system,for example.

REFERENCE SIGNS LIST

-   100, 300, 400, 500 terminal-   200 base station-   101 RS generation section-   102 phase rotation section-   103 mapping section-   104 IFFT section-   105 CP addition section-   106, 208, 301, 402, 501 offset setting section-   107 elapsed-time calculation section-   108, 303, 503 offset value determination section-   109 transmission section-   110 D/A section-   111 transmission power control section-   112 up-conversion section-   113, 201 antenna-   202 reception section-   203 CP removal section-   204 FFT section-   205 demapping section-   206 cyclic shift amount setting section-   207 SRS SINR measurement section-   209 data SINR deriving section-   210 channel quality deriving section-   302 power difference calculation section-   401 transmission processing section-   502 SRS-type determination section

The invention claimed is:
 1. A terminal apparatus comprising: areference signal generating section configured to generate a firstSounding Reference Signal (SRS) with a first transmission time intervaland a second SRS with a second transmission time interval, the secondtransmission time interval being different from the first transmissiontime interval, both of the first SRS and the second SRS being referencesignals for channel-quality estimation; an offset setting sectionconfigured to set a first offset value to control transmission powerused to transmit the first SRS and to set a second offset value tocontrol transmission power used to transmit the second SRS, secondoffset value being different from the first offset value; and atransmitting section configured to transmit the first SRS with thetransmission power controlled based on the first offset value and totransmit the second SRS with the transmission power controlled based onthe second offset value.
 2. The terminal apparatus according to claim 1,wherein the offset setting section sets a greater offset value for alonger transmission time interval.
 3. The terminal apparatus accordingto claim 2, wherein the offset setting section sets each of the firstand the second offset values by adding a correction value to atransmission power offset value specified by a base station apparatus.4. The terminal apparatus according to claim 1, wherein the offsetsetting section sets each of the first and the second offset values byadding a correction value to a transmission power offset value specifiedby a base station apparatus.
 5. The terminal apparatus according toclaim 1, wherein the first SRS is a periodic SRS which is transmittedperiodically, and a second SRS is an aperiodic SRS which is transmittedaperiodically.
 6. The terminal apparatus according to claim 5, whereinthe offset setting section sets the second offset value to be greaterthan the first offset value.
 7. A method of controlling transmissionpower of a reference signal, the method comprising: generating a firstSounding Reference Signal (SRS) with a first transmission time intervaland a second SRS with a second transmission time interval, the secondtransmission time interval being different from the first transmissiontime interval, both of the first SRS and the second SRS being referencesignals for channel-quality estimation; setting a first offset value tocontrol transmission power used to transmit the first SRS and to set asecond offset value to control transmission power used to transmit thesecond SRS, the second offset value being different from the firstoffset value; and transmitting the first SRS with the transmission powercontrolled based on the first offset value and transmitting the secondSRS with the transmission power controlled based on the second offsetvalue.
 8. The method according to claim 7, wherein a greater offsetvalue is set for a longer transmission time interval.
 9. The methodaccording to claim 8, wherein each of the first and the second offsetvalues is set by adding a correction value to a transmission poweroffset value specified by a base station apparatus.
 10. The methodaccording to claim 7, wherein each of the first and the second offsetvalues is set by adding a correction value to a transmission poweroffset value specified by a base station apparatus.
 11. The methodaccording to claim 7, wherein the first SRS is a periodic SRS which istransmitted periodically, and a second SRS is an aperiodic SRS which istransmitted aperiodically.
 12. The method according to claim 11, whereinthe second offset value is set to be greater than the first offsetvalue.